At the end of the last chapter of the book, Aunt Eva tells Hannah that she and Grandpa Will, along with many other concentration camp survivors, changed their names when they came to America because they wanted "to forget."
Aunt Eva tells Hannah that "remembering was too painful." By this, Aunt Eva means that their old names reminded them of their persecution as Jews and specifically of the torments and horrors that they endured in the Nazi concentration camps. Aunt Eva explains to Hannah that their experiences in the concentration camps were so horrific that it became difficult to associate anything other than those experiences with their old names. Aunt Eva says that she, Grandpa Will, and the others therefore changed their names in an effort to forget the pain of the past. Aunt Eva also says, however, that these efforts were in vain and that, ultimately, "to forget was impossible."
After World War II, many of the Jews who emigrated to America really did change their names. Many perhaps, like Aunt Eva, did so in an effort to dispel the memories associated with those names, but many did so also because of the anti-Semitic attitudes they faced upon arriving in America.
Aunt Eva tells Hannah that she, Aunt Eva, used to be called Rivka when she was in the concentration camp. She says that Grandpa Will, despite being "as gentle as a lamb," used to be called Wolfe.